Recent engineering studies show that electrical signals can be transmitted through a human body. With careful configuration, these signals can be modulated to carry digital information across a so-called “Body-Area Network” (“BAN”).
One company, for example, makes small ingestible pills. Each pill contains the circuitry for a transmitter. When the outer covering of the pill dissolves in a digestive tract, contacts are exposed to stomach acid. The stomach acid acts as a dielectric to power the transmitter. (For safety's sake, the pill contains no other power source.) When powered up, the transmitter repeatedly sends out a weak electrical signal. The signal is carried across the BAN to a receiving device located outside, but in physical contact with, the ingestor's body. The receiver demodulates the signal into an identification code. The transmitter continues to send out its signal until the process of digestion dissolves the pill. The transmitter typically transmits for a total of five to seven minutes.